The present invention relates to catheters for performing tissue ablation and, in particular, it concerns a multiple-electrode catheter assembly and a method of using a multiple-electrode catheter assembly.
Atrial fibrillation is, in many cases, treated by ablating atrial tissue at a plurality of locations along a line so as to form a closed loop of ablation across the atrium. In other cases, it is treated by ablating the pulmonary vein tissue at a plurality of locations along a line, so as to form a closed loop of ablation across the vein.
PCT Publication No. WO00/16684, which is incorporated by reference as if fully set forth herein, teaches how to mark and ablate a series of points of ablation in order to create a continues line of ablation. According to WO00/16684 this is effected by a steerable catheter having a tip adapted to ablate a single point. It is very difficult, however, to achieve sufficient precision to ensure ablation of a contiguous line of tissue using a single electrode catheter. Furthermore, the repeated repositioning of the catheter between successive ablation steps is very time consuming.
In an alternative approach to ablation of a line of tissue, a number of multiple-electrode catheters have been proposed to allow successive ablation of multiple sites while the catheter is in a single position. Examples of such devices may be found in U.S. Pat. Nos. 5,842,984; 5,555,883; 5,893,885; 5,433,198 and 5,341,807, which are incorporated by reference as if fully set forth herein. Each of these teaches a multiple-electrode catheter designed to ablate a tissue at a plurality of locations along a line of predetermined configuration. In some cases, this configuration is monitored by sensors adapted for determining the shape or curvature of the portion of the catheter carrying the multiple electrodes. These multiple-electrode catheters are positioned in contact with the endocardium tissue where ablation is performed in a controlled manner, typically one electrode at a time. Typically, the parameters of the process, such as current, voltage, and temperature are monitored at each individual point of ablation, thereby giving an indication of the quality of ablation at each point.
Although the use of a multiple-electrode catheter provides a partial solution to the difficulty in forming a contiguous line of ablation, significant problems are still encountered. Most significantly, it often occurs that one or more of the electrodes is not properly in contact with the endocardium when actuated and, as a result, insufficient ablation occurs. This results in a break in the line of ablation which may cause the entire procedure to fail. In order to facilitate re-treatment of a site not properly treated by the device, it is possible to include multiple location sensing elements adjacent to the electrodes to record the position of each point treated. This however, would add very greatly to the cost of the device. Finally, even without multiple location sensing elements, the structure of a multiple-electrode catheter is complicated by the need for multiple electrical wires along the entire length of the catheter and corresponding multiple electrical connections. Each electrode requires its own electrical connection. Furthermore, if a thermistor is to be provided for each electrode, a further two wires are required. As a result, a ten electrode catheter typically requires 30 wires passing along its length. This presents a considerable design problem for a catheter of a few millimeters diameter, and results in high production costs. Since such catheters are typically disposable items intended for a single use, the use of such catheters adds significantly to the cost of the procedure.
There is therefore a need for a multiple-electrode catheter assembly and method of operating such a catheter assembly which would ensure reliable contact between each electrode and the corresponding region of tissue during actuation of the electrode.